What cannot be undone
Almost everything that goes wrong while flashing is fixed by writing the official fastboot ROM back. The exceptions are few, and the two below account for nearly all of them. Both can only be avoided before you flash.
Anti-Rollback (ARB) violation unrecoverable
What happens: An ARB index is burned into the chipset's eFuse storage. Flashing firmware whose ARB index is lower than the one currently burned sets a permanent fuse.
Result: The device stops booting and cannot be recovered by any software or hardware method. No repair shop can fix it.
How you get there: Downgrading firmware. Most often: 'going back to the last stable build', or flashing an older ROM from a different region.
How to avoid it: Confirm that the ARB index of the ROM you are about to flash is greater than or equal to the one currently on the device. If you cannot confirm it, do not flash.
Dropping to EDL (9008) without an authorized account not recoverable by you
What happens: If the device boots neither the system nor fastboot, writing from EDL (Emergency Download Mode) is the only route left. Since 2018 Xiaomi has restricted EDL writes to authorized Mi Accounts.
Result: End users cannot recover the device themselves. It becomes a paid repair-shop job.
How you get there: Operations that break the partition layout; the cable coming loose or the PC sleeping mid-flash; flashing firmware that does not match the device.
How to avoid it: Do not let the PC sleep during a flash. Use a cable that actually carries data. Charge above 50% first.
Relocking the bootloader while a custom ROM is installed usually recoverable
What happens: Custom ROMs are signed with different keys. Relocking makes Verified Boot detect the signature mismatch and refuse to boot.
Result: The device will not boot. If fastboot still responds you can flash the official ROM and recover; if fastboot is gone too, you are in the EDL case above.
How you get there: Relocking to satisfy banking apps or Play Integrity while still running a custom ROM.
How to avoid it: Only relock immediately after flashing the official fastboot ROM back (flash_all_lock).
Sources: [1]
What is recoverable
Download the official fastboot ROM and write it with flash_all. Use flash_all_lock if you also want the bootloader closed. You start over from the Mi Account setup.
Caveat: Pick a ROM whose ARB index is greater than or equal to the current one. Getting this wrong puts you in the arb case above.
Sources: [1]
What unlocking costs you
None of these break the device, but they take effect the moment the bootloader is unlocked, and relocking does not always bring them back. The last three depend on where the device was sold.
| Item | Detail |
|---|---|
| HyperOS OTA updates | Devices with an unlocked bootloader do not receive official HyperOS updates. Sources: [1] |
| Play Integrity | Banking, payment and some games stop working, because Verified Boot is no longer intact. |
| Widevine L1 | May drop to L3, which caps streaming services below HD. |
| FeliCa / Osaifu-Keitai JP models | Present only on Japanese-market models. Flashing a global or custom ROM removes it, and it is not restored by going back to stock in every case. |
| Carrier features and band configuration region-specific | VoLTE/VoWiFi profiles and band tables ship per region. A ROM from another region can silently drop calling or a band your local carrier depends on. Worst affected: devices bought abroad and used on a domestic network. |
| Manufacturer warranty | May be void from the moment the bootloader is unlocked. |
Whether you can unlock at all
Since 2025 the path to an unlocked bootloader has narrowed substantially.
- A minimum activity level on the Xiaomi Community app is required
- A knowledge quiz must be passed
- Application slots are capped and can fill at 00:00 GMT+8 ('quota limit reached')
- One device per account per year
- Approval takes 3–7 days
Devices sold in mainland China carry additional account-binding restrictions beyond the global rules. Hong Kong, Macau and Taiwan units follow the non-CN path.
Which layers actually change
It is tempting to assume that because HyperOS is itself a modified Android, a third party can replace the whole stack. It cannot. Only the top layer is in reach.
| Layer | Third party | Notes |
|---|---|---|
| Bootloader / xbl, abl, modem, trustzone | locked | Xiaomi-signed. Not what a custom ROM replaces. |
| Vendor / firmware blobs | locked | Only images from an official fastboot ROM are accepted. |
| Android OS (boot / system / product) | writable | This is the only layer a custom ROM replaces. |
ROM types and what "open source" means here
Whether "it's open source, so it's safe" holds depends entirely on which of these you mean.
The only ROM Xiaomi signs. It is also the only one with access to every layer, including the bootloader, modem and trustzone.
An official ROM modified and re-signed by a small independent team. No source is published. It is the most common 'custom ROM' recommendation outside China, and installing it means granting system-level trust to a third-party build nobody can audit.
Source is published and reviewable. Camera, modem and DRM vendor blobs remain closed binaries, so it is not fully open source. Most devices also require a specific stock firmware to be installed first — a vendor SPL mismatch breaks the camera and other hardware.
Independently of any of that: unlocking the bootloader disables Verified Boot. Whatever you flash, you are choosing to run a device that no longer checks itself at boot.